Christoph Heyl

Helmholtz-Institut Jena & DESY, Hamburg

Nonlinear optical methods have become ubiquitous in many scientific areas, from fundamental studies of time-resolved electron dynamics to microscopy and spectroscopy applications. They are, however, often limited to a certain range of parameters such as pulse energy and average power. Restrictions arise from, for example, the required field intensi...

Laser-driven high-order harmonic generation (HHG) provides tabletop sources of broadband extreme-ultraviolet (XUV) light with excellent spatial and temporal coherence. These sources are typically operated at low repetition rates, $f_{rep}\lesssim$100 kHz, where phase-matched frequency conversion into the XUV is readily achieved. However, there are...

In this work, we demonstrate postcompression of 1.2 ps laser pulses to 13 fs via gas-based multipass spectral broadening. Our results yield a single-stage compression factor of about 40 at 200 W in-burst average power and a total compression factor >90 at reduced power. The employed scheme represents a route toward compact few-cycle sources driven...

Ultrafast lasers reaching extremely high powers within short fractions of time enable a plethora of applications. They grant advanced material processing capabilities, are effective drivers for secondary photon and particle sources, and reveal extreme light-matter interactions. They also supply platforms for compact accelerator technologies, with g...

The serrodyne principle enables an electromagnetic signal to be frequency shifted by applying a linear phase ramp in the time domain. This phenomenon has been exploited to frequency shift signals in the radiofrequency, microwave and optical regions of the electromagnetic spectrum over ranges of up to a few gigahertz, for example, to analyse the Dop...

Advancing ultrafast high-repetition-rate lasers to shortest pulse durations comprising only a few optical cycles while pushing their energy into the multi-millijoule regime opens a route toward terawatt-class peak powers at unprecedented average power. We explore this route via efficient post-compression of high-energy 1.2 ps pulses from an ytterbi...

Advancing ultrafast high-repetition-rate lasers to shortest pulse durations comprising only a few optical cycles while pushing their energy into the multi-millijoule regime opens a route towards terawatt-class peak powers at unprecedented average power. We explore this route via efficient post-compression of high-energy 1.2 ps pulses from an Ytterb...

Frequency combs present a unique tool for high-precision and rapid molecular spectroscopy. Difference frequency generation (DFG) of near-infrared sources is a common approach to generate passively stabilized mid-infrared combs. However, only little attention has been paid so far to precisely measure the coherence properties of such sources. Here, w...

Control over intensity, shape, direction, and phase of coherent light is essential in numerous fields, reaching from gravitational wave astronomy over quantum metrology and ultrafast sciences to semi-conductor fabrication. Modern laser optics, however, frequently demands parameter regimes where either the wavelength or the optical power restricts c...

The generation of below-threshold harmonics in gas-jets constitutes a promising path towards optical frequency combs in the vacuum ultra-violet (VUV) spectral range. Of particular interest is the 150 nm range, which can be exploited to probe the nuclear isomeric transition of the Thorium-229 isotope. Using widely available high-power, high-repetiti...

Post-compression methods for ultrafast laser pulses typically face challenging limitations, including saturation effects and temporal pulse breakup, when large compression factors and broad bandwidths are targeted. To overcome these limitations, we exploit direct dispersion control in a gas-filled multi-pass cell, enabling, for the first time to th...

We demonstrate efficient post compression of 9.45 mJ, 1.2 ps pulses to 13 fs at 1 kHz repetition rate using a two stage gas filled multi pass cell system reaching near terawatt peak power.

Few-cycle pulses present an essential tool to track ultrafast dynamics in matter and drive strong field effects. To address photon-hungry applications, high average power lasers are used which, however, cannot directly provide sub-100-fs pulse durations. Post-compression of laser pulses by spectral broadening and dispersion compensation is the most...

Few-cycle pulses present an essential tool to track ultrafast dynamics in matter and drive strong field effects. To address photon-hungry applications, high average power lasers are used which, however, cannot directly provide sub-100 fs pulse durations. Post-compression of laser pulses by spectral broadening and dispersion compensation is the most...

High-order harmonic generation (HHG) in gases leads to short-pulse extreme ultraviolet (XUV) radiation that is useful in a number of applications, such as attosecond science and nanoscale imaging. However, this process depends on many parameters, and there is still no consensus on how to choose the target geometry to optimize the source efficiency....

The serrodyne principle enables shifting the frequency of an electromagnetic signal by applying a linear phase ramp in the time domain [1]. This phenomenon has been exploited to frequency-shift signals in the radiofrequency (RF), microwave and optical region of the electromagnetic spectrum over ranges of up to a few GHz e.g. to analyse the Doppler...

Tailoring the properties of the driving laser to the need of applications often requires compromises among laser stability, high peak and average power levels, pulse duration, and spectral bandwidth. For instance, spectroscopy with optical frequency combs in the extreme/visible ultraviolet spectral region requires a high peak power of the near-IR d...

Post-compression of ultra-short laser pulses via self-phase modulation is routinely employed for the generation of laser pulses with optical bandwidths reaching far beyond the laser gain limitations. Although high compression factors can be routinely achieved, the compressed pulses typically suffer from temporal quality degradation. We numerically...

We report the broadband absorption spectrum of the $3\nu_{2}$ band of $^{14}$NH$_{3}$ near 4 $\mu m$. The data was recorded using a mid-infrared frequency comb coupled to a homebuilt Fourier-transform spectrometer with a resolution of 0.00501 $cm^{-1}$. Line positions, self-broadening, and self-shift parameters for six rovibrational lines were dete...

As ultrafast laser technology advances towards ever higher peak and average powers, generating sub-50 fs pulses from laser architectures that exhibit best power-scaling capabilities remains a major challenge. Here, we present a very compact and highly robust method to compress 1.24 ps pulses to 39 fs by means of only a single spectral broadening st...

High-order harmonic generation (HHG) in gases leads to short-pulse extreme ultraviolet (XUV) radiation useful in a number of applications, for example, attosecond science and nanoscale imaging. However, this process depends on many parameters and there is still no consensus on how to choose the target geometry to optimize the source efficiency. Her...

The Free‐Electron Laser (FEL) FLASH offers the worldwide still unique capability to study ultrafast processes with high‐flux, high‐repetition rate extreme ultraviolet, and soft X‐ray pulses. The vast majority of experiments at FLASH are of pump–probe type. Many of them rely on optical ultrafast lasers. Here, a novel FEL facility laser is reported w...

Post-compression of ultra-short laser pulses via self-phase modulation is routinely employed for the generation of laser pulses with optical bandwidths reaching far beyond the laser gain limitations. While high compression factors can be routinely achieved, the compressed pulses typically suffer from temporal quality degradation. We numerically and...

We demonstrate a 41.6 MHz, 1.3 ps, 140 pJ Ho:fiber oscillator using a nonlinear amplifying loop mirror (NALM) as saturable absorber. The oscillator is constructed entirely with polarization-maintaining (PM) fibers, is tunable with a center wavelength between 2035 nm and 2075 nm, and can be synchronized to an external RF reference. For our applicati...

Multi-pass cells have emerged as very attractive tools for spectral broadening and post-compression applications. We discuss pulse energy limitations of standard multi-pass cells considering basic geometrical scaling principles and introduce a novel energy scaling method using a multi-pass cell arranged in a bow tie geometry. Employing nonlinear pu...

We demonstrate sub-20 fs single-stage post-compression of an Ytterbium-doped fiber laser. Dispersion-engineered dielectric cavity mirrors are used to control spectral broadening in a gas-filled multi-pass cell supporting a throughput of 98%.

We present recent developments of Yb-fiber laser front-ends tailored for a variety of special needs for high repetition rate accelerator driven FEL and UED facilities.

We report on 100-W 132 MHz Yb:fiber amplifier seeded by a low noise oscillator. We tune the laser spectrum to match it to different applications while keeping noise properties and power performance of the system.

We introduce a new concept to frequency shift a high-power laser using a waveshaper and a multi pass cell. We demonstrate this concept by experimentally frequency shifting a 200 fs laser from 1030 nm to 1000 nm.

We demonstrate an all-PM high power ultrafast Yb-fiber laser utilizing digital controls for frequency comb stabilization and femtosecond pulse shaping.

We discuss basic pulse energy scaling principles for multi-pass cells (MPCs) and introduce a novel multi-pass cell type which we employ to numerically predictpost-compression of 125 mJ pulses using a 2 m setup.

We present a wavelength shifting method suitable for high power lasers. We demonstrate our concept via simulations and experimentally shift an 80 W, 200 fs laser at 1030 nm by ±30 nm.

We introduce the bow tie multi-pass cell as a new scheme for post-compression of high-energy laser pulses, overcoming current limits of Herriott-type multi-pass cell-based postcompression imposed mainly by mirror damage threshold limitations.

We present the design, integration, and operation of the novel vacuum ultraviolet (VUV) beamline installed at the free-electron laser (FEL) FLASH. The VUV source is based on high-order harmonic generation (HHG) in gas and is driven by an optical laser system synchronized with the timing structure of the FEL. Ultrashort pulses in the spectral range...

As Ultrafast laser technology advances towards ever higher peak and average powers, generating sub-50 fs pulses from laser architectures that exhibit best power-scaling capabilities remains a major challenge. Here, we present a very compact and highly robust method to compress 1.24 ps pulses to 39 fs by means of only a single spectral broadening st...

Nonlinear pulse post-compression represents an efficient method for ultrashort, high-quality laser pulse production. The temporal pulse quality is, however, limited by amplitude and phase modulations intrinsic to post-compression. We here characterize in frequency and time domain with high dynamic range individual post-compressed pulses within lase...

We present a comparison of two low-noise carrier-envelope offset (CEO) frequency stabilization methods studied using an ytterbium (Yb) fiber laser oscillator based on a nonlinear amplifying loop mirror. We first investigate the phase locking performance achieved with cross-gain modulation (XGM) via injection of an auxiliary low-power continuous-wav...

The Free-Electron Laser (FEL) FLASH offers the worldwide still unique capability to study ultrafast processes with high-flux, high-repetition rate XUV and soft X-ray pulses. The vast majority of experiments at FLASH are of pump-probe type. Many of them rely on optical ultrafast lasers. Here, a novel FEL facility laser is reported which combines hig...

We report a simple and compact design of a dispersion compensated mode-locked Yb:fiber oscillator based on a nonlinear amplifying loop mirror (NALM). The fully polarization maintaining (PM) fiber integrated laser features a chirped fiber Bragg grating (CFBG) for dispersion compensation and a fiber integrated compact non-reciprocal phase bias device...

We report a simple and compact design of a dispersion compensated mode-locked Yb:fiber oscillator based on a nonlinear amplifying loop mirror (NALM). The fully polarization maintaining (PM) fiber integrated laser features a chirped fiber Bragg grating (CFBG) for dispersion compensation and a fiber integrated compact non-reciprocal phase bias device...

This talk provides a review of laser pulse post-compression leveraged by the advent of the multi-pass spectral broadening scheme, including perspectives on expanding the limits of pulse duration and energy.

We demonstrate an all-PM fiber integrated femtosecond Yb NALM oscillator with 88 fs compressed pulse duration and sub-fs free-running timing jitter [25 kHz to 5 MHz].

We report on pulse contrast characterization of the output of a gas-filled multi-pass cell employed for 20-fold compression of a high-power Yb:YAG laser. We demonstrate an energy content of 80% in the compressed fs pulse.

We introduce the combination of multi-pass cell and multi-plate spectral broadening. We demonstrate the compression of 110-μJ pulses from 900-fs to 60-fs in a single stage and report broadening to 38-fs transform-limit by nonlinear mode-matching.

We demonstrate a 41.6 MHz, 1.3 ps, 140 pJ Ho:fiber oscillator centered at 2050 nm for seeding Ho:YLF amplifiers. RIN and timing jitter of the oscillator are characterized while comparing two commercial Tm pump lasers.

We demonstrate single-stage post-compression of an Ytterbium fiber laser to about 20 fs based on spectral broadening in a gas-filled multipass cell. A compression factor of seven has been achieved with a throughput of 86%.

We present high-power Yb:YAG lasers combined with nonlinear pulse compression in multi-pass cells. We show that these are suitable for integration in FEL facilities in terms of pulse stability, jitter, temporal contrast and intra-burst behaviour.

We demonstrate post-compression of a high energy Yb:YAG laser in a 2m long Argon-filled multi-pass cell (MPC). 1.2 ps pulses with 8.6 mJ are compressed to 44 fs with an MPC transmission of 93%.

This paper reports on nonlinear spectral broadening of 1.1 ps pulses in a gas-filled multi-pass cell to generate sub-100 fs optical pulses at 1030 nm and 515 nm at pulse energies of 0.8 mJ and 225 µJ, respectively, for pump–probe experiments at the free-electron laser FLASH. Combining a 100 kHz Yb:YAG laser with 180 W in-burst average power and a p...

We demonstrate a femtosecond enhancement cavity with a crossed-beam geometry for efficient generation and extraction of extreme-ultraviolet (XUV) frequency combs at a 154 MHz repetition rate. We achieve a record-high out-coupled power of 600 μW, directly usable for spectroscopy, at a wavelength of 97 nm. This corresponds to a >60% out-coupling effi...

We present a flexible all-polarization-maintaining (PM) mode-locked ytterbium (Yb):fiber laser based on a nonlinear amplifying loop mirror (NALM). In addition to providing detailed design considerations, we discuss the different operation regimes accessible by this versatile laser architecture and experimentally analyze five representative mode-loc...

Ultrafast measurements in the extreme ultraviolet (XUV) spectral region targeting femtosecond timescales rely until today on two complementary XUV laser sources: free electron lasers (FELs) and high-harmonic generation (HHG) based sources. The combination of these two source types was until recently not realized. The complementary properties of bot...

We present a flexible all-polarization-maintaining (PM) mode-locked ytterbium (Yb):fiber laser based on a nonlinear amplifying loop mirror (NALM). In addition to providing detailed design considerations, we discuss the different operation regimes accessible by this versatile laser architecture and experimentally analyze five representative mode-loc...

In this work, we demonstrate post-compression of 1.2 picosecond laser pulses to 13 fs via gas-based multi-pass spectral broadening. Our results yield a single-stage compression factor of about 40 at 200 W in-burst average power and a total compression factor >90 at reduced power. The employed scheme represents a route towards compact few-cycle sour...

We demonstrate a femtosecond enhancement cavity with a crossed-beam geometry for efficient generation and extraction of extreme-ultraviolet (XUV) frequency combs at 154 MHz repetition rate. We achieve a record-high out-coupled power of 600 {\mu}W, directly usable for spectroscopy, at a wavelength of 97 nm. This corresponds to a >60% out-coupling ef...

We present a HHG-based vacuum ultraviolet (VUV) source at the free electron laser FLASH2. The source provides ultrashort pulses from 10 to 40eV, coupled to the REMI end-station (beamline FL26) for VUV-FEL pump-probe experiments.

We present a versatile all-PM Yb:fiber-laser and demonstrate the impact of dispersion engineering on amplitude/phase noise and the carrier-envelope-offset frequency, whose linewidth can be reduced from several MHz down to single-digit-kHz values in free-running operation.

We report nonlinear pulse compression of 1.2-ps, 2-mJ pulses. For spectral broadening, we use a Kr-filled Herriott-type cell with 22-roundtrips. After a chirped-mirror compressor, we measure 30-fs pulses, 80% transmission and an M ² of 1.5×1.7.

We demonstrate a fully integrated alignment free, femtosecond Yb:fiber laser operating in the stretched pulse regime. After compression, the laser provides a long-term stable output of 104 fs pulses at 76 MHz repetition rate.

We present a VUV beamline installed as pump-probe source at the free-electron laser FLASH. The source is based on high-order harmonic generation driven by femtosec-ond near-infrared laser pulses synchronized with the FEL burst mode.